This application relates to damping torsional oscillation, and more specifically to an electric load damper for damping torsional oscillation.
Synchronous generators are used in a variety of applications to convert mechanical energy provided by an engine to alternating current (“AC”) electrical energy. One example application for a synchronous generator is a gas turbine engine for an aircraft, in which the generator generates AC electrical energy to operate on-board electrical systems.
A gas turbine engine may be used to generate mechanical energy that is provided through a gearbox along a shaft to one or more synchronous generators. Due to a multitude of competing mechanical design considerations, the shaft may be relatively long and mechanically compliant. The inertias associated with the engine, the gearbox, the one or more synchronous generators, and other gearbox driven accessories in combination with the mechanical compliance or spring rates of the mechanical drive train, including the generator shaft, may create a distributed mechanical spring-mass system that exhibits torsional oscillation.
Engine gearboxes may exhibit lightly damped characteristics, resulting in overall negative damping when coupled to a high power generator or generators due to their electromechanical torque characteristics for disturbance frequencies that are within the generator's voltage regulation bandwidth. In certain situations, depending on factors such as generator speed, generator electrical load, and net effective damping in the overall mechanical drive train, the torsional resonance of the spring-mass system involving the generator or generators can lead to large, undesirable torsional oscillations and mechanical failures in the system. Although mechanical damping may be used to offset the negative damping characteristic of the synchronous generator or generators and thus dampen the torsional oscillations in the spring-mass system, mechanical damping requires additional hardware and mechanical components that can increase the weight and cost of a system.